Field of the Invention
One disclosed aspect of the embodiments relates to a solid-state image pickup device, and more particularly to an amplifier circuit which amplifies signals.
Description of the Related Art
In a typical solid-state image pickup device, pixels are arranged in a matrix form and constitute an image pickup area. An amplifier circuit is provided for each column of pixels or every plural columns of pixels. U.S. Pat. No. 5,892,540 discloses an exemplary configuration of a solid-state image pickup device. An amplifier circuit is provided in each column of pixels. The amplifier circuit is a two-stage column amplifier circuit consists of a preceding variable-gain amplifier circuit and a subsequent voltage follower amplifier.
In a solid-state image pickup device, it is required that a signal generated in a photoelectric converter is amplified at high gain as quickly as possible. This is because, if a signal is amplified at high gain before noise is superimposed on the signal, an S/N ratio is increased. Recently, therefore, it is required to amplify a signal at an even higher gain in the column amplifier circuit. In a configuration in which a gain is applied to a signal only at a preceding amplifier circuit and a subsequent amplifier circuit is used as a buffer, as in the device disclosed U.S. Pat. No. 5,892,540, there is a possibility that the preceding amplifier circuit has a complicated circuit configuration and is thus not received within a predetermined pixel pitch. In view of the aforementioned, one aspect of the embodiments enables amplification at high gain by a simple configuration in an amplifier circuit provided on, for example, a column of pixels.